首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   544篇
  免费   31篇
  国内免费   13篇
儿科学   18篇
妇产科学   2篇
基础医学   44篇
口腔科学   10篇
临床医学   23篇
内科学   83篇
皮肤病学   10篇
神经病学   43篇
特种医学   6篇
外科学   30篇
综合类   63篇
预防医学   55篇
眼科学   1篇
药学   135篇
中国医学   51篇
肿瘤学   14篇
  2023年   7篇
  2022年   15篇
  2021年   20篇
  2020年   13篇
  2019年   20篇
  2018年   20篇
  2017年   6篇
  2016年   9篇
  2015年   14篇
  2014年   20篇
  2013年   34篇
  2012年   37篇
  2011年   20篇
  2010年   16篇
  2009年   19篇
  2008年   19篇
  2007年   25篇
  2006年   21篇
  2005年   15篇
  2004年   18篇
  2003年   19篇
  2002年   15篇
  2001年   7篇
  2000年   11篇
  1999年   5篇
  1998年   7篇
  1997年   8篇
  1996年   9篇
  1995年   10篇
  1994年   9篇
  1993年   6篇
  1992年   6篇
  1991年   3篇
  1990年   7篇
  1989年   7篇
  1988年   4篇
  1987年   6篇
  1986年   5篇
  1985年   3篇
  1984年   13篇
  1983年   9篇
  1982年   10篇
  1981年   9篇
  1980年   7篇
  1979年   3篇
  1978年   5篇
  1977年   2篇
  1975年   4篇
  1974年   4篇
  1973年   2篇
排序方式: 共有588条查询结果,搜索用时 15 毫秒
1.
Separation of the external membranes from freshly converted mechanical schistosomula of Schistosoma mansoni was achieved by osmotic shock under hypertonic conditions, followed by mechanical shearing and ultracentrifugation. Prior to treatment, the schistosomula were surface labeled by introduction of N-DNP-epsilon-aminocaproylphosphatidylethanolamine molecules into their lipid bilayer followed by anti-DNP antibodies and stained with either 125I-protein-A or ferritin labeled secondary anti-DNP antibodies. This label provided a membrane marker by which the purity of the preparation could be assessed at each stage. Fluorescence staining with FITC-conjugated secondary antibodies prior to treatment revealed that the homogeneously stained membrane of the intact schistosomula became swollen and ruptured after the osmotic shock. The isolated membrane pellet was intensely fluorescent. Electron microscopical examination revealed mostly vesicles, some of them with organized multilayer assembly. The vesicles were ferritin labeled, indicating that they originated from the outer surface membrane of the schistosomula. A 100 fold enrichment in the alkaline phosphatase activity and about 300 fold enrichment in acetylcholinesterase activity in the membrane preparations, as compared to the intact schistosomula, was found. The isolated tegument was analyzed by SDS-polyacrylamide gel electrophoresis. The pattern obtained showed three major bands, of molecular weights 69 000, 45 000 and 12 000 alongside with a large number of minor bands. Immunoprecipitation of the isolated 125I-labeled membrane antigens with antisera from chronically infected mice revealed these three major bands together with three other bands of molecular weight 38 000, 23 000 and 16 000.  相似文献   
2.
用苯酚、苯酐和水合肼合成了4-(4-羟苯基)-2,3-二氮杂萘酮-1,并与双酚-A和二苯甲酮聚合,得到含双酚-A和杂环结构的聚醚酮聚合物。用FT-IR、^13C-NMR、DSC、TGA和DMA等方法对聚合物进行了表征。结果表明,这种可溶性的非晶态聚合物有较高的Tg和很高的耐热温度,Tg随聚合物的组成不同而变化(158-224℃),5%热失重温度为444-541℃。  相似文献   
3.
运用彗星试验检测麝香酮对苯并(a)芘致DNA损伤的影响   总被引:1,自引:0,他引:1  
[目的]研究麝香酮在体内试验条件下 ,对苯并(a)芘致小鼠肝和肺细胞核DNA损伤的影响。[方法]SENCAR雄性成年小鼠灌胃 ,分别单独给予苯并(a)芘125、250、500mg/(kg·bw·d)和用麝香酮250、500mg/(kg·bw·d)预处理后再给予苯并(a)芘125mg/(kg·bw·d) ,处死动物后分离小鼠肝和肺组织细胞核做彗星测试 ,采用CCD成像分析系统分析彗星 ,取尾相 (olivertailmoment,OTM)值判断DNA损伤强度。[结果]苯并(a)芘各浓度组均出现小鼠肝和肺细胞OTM值的明显增加 ,高浓度麝香酮[500mg/(kg·bw·d)]可引起小鼠肝细胞OTM值的轻度增加。用高浓度麝香酮预处理小鼠后再给予苯并(a)芘 ,所观察到的肝、肺的DNA损伤 (肝OTM值为7.6、肺为11)较之苯并(a)芘单独染毒引起的DNA损伤(肝OTM值为5.1、肺为6.9)增加更明显。[结论]麝香酮能明显增强苯并(a)芘所致的DNA损伤作用  相似文献   
4.
对聚醚醚酮/二苯砜、聚醚醚酮/二苯酮所组成聚合物/稀释剂体系,采用热致相分离法制备了聚醚醚酮多孔膜,探讨了制备具有耐高温、耐溶剂的聚醚醚酮多孔膜的可能性,对聚合物/稀释剂体系的相容性进行理论计算和分析,并研究了聚合物的含量对成膜多孔结构的影响。  相似文献   
5.
The aim of this study was to assess two new protocols for single-stage rehabilitation of the severely atrophic maxillary ridge using customized porous titanium or polyether ether ketone (PEEK) sub-periosteal implants. Ten patients with a severely atrophic anterior maxillary alveolar ridge were divided randomly into two groups (five patients in each) to receive customized sub-periosteal implants fabricated via CAD/CAM technology: group 1, porous titanium implants; group 2, PEEK implants. Prosthetic loading with fixed acrylic bridges was performed 1 month postoperative. The implants were followed-up for 12 months and evaluated for the presence of any sign of radiographic bone resorption, mobility, infection, prosthetic fracture, or implant exposure. The immediate postoperative period was uneventful except for one case complicated by wound dehiscence in group 1. At 12 months, all implants were functionally stable and the patients were comfortable with the prostheses. No signs of radiographic bone resorption, mobility, infection, or prosthetic fracture were observed. Within the limitations of this study, the application of customized porous titanium and PEEK sub-periosteal implants produced through CAD/CAM technology appears to be an acceptable method for single-stage prosthetic rehabilitation of the severely atrophic edentulous anterior maxilla.This study was awarded the best case study at the academy of osseintegration annual meeting 2017, Orlando, Florida.  相似文献   
6.
The arterial ketone body ratio (acetoacetate to β-hydroxybutyrate) was measured in 15 patients with chronic liver disease before and after the infusion of anticancer drugs or embolic agents (gelatin sponge or iodized oil) into the hepatic artery. The arterial ketone body ratio decreased after hepatic angiography and decreased further at 15 min after infusion therapy. When the arterial ketone body ratio decreased to 1.0 or less on at least one occasion after infusion therapy, the ratio after hepatic angiography was always 1.35 or less. Such patients developed marked systemic symptoms like fever and severe liver dysfunction. Ascites also developed in three patients in whom the arterial ketone body ratio was reduced to 0.7 or less at 24 h after infusion therapy. The arterial ketone body ratios improved at 3–7 days after infusion therapy. In the seven patients treated with gelatin sponge embolization, the ratio at 3–7 days after therapy was actually higher than that before angiography.  相似文献   
7.
Summary In 5 closely controlled pregnant diabetics (duration of pregnancy 237–266 days) and 5 pregnant non-diabetics (duration of pregnancy 210–278 days) 4-hourly blood samples were taken throughout a 24 h period and analyzed for blood glucose, lactate, pyruvate, 3-hydroxybutyrate and acetoacetate, plasma non-esterified fatty acids (NEFA), glucagon and cortisol. 24 h urine specimen was analyzed for total catecholamines and 4-hydroxy-3-methoxymandelic acid. There were few significant differences in concentrations of metabolites and hormones in the two groups at any time, although the variations about the mean was usually greater in the diabetics. Thus for blood glucose in diabetics, mean value was 4.4 mmol/l, coefficient of variation 43%; in non-diabetics 4.1 mmol/l and 10% respectively. Mean plasma 3-hydroxybutyrate in diabetics was 0.47 mmol/l, coefficient of variation 55%; in non-diabetics 0.44 mmol/l and 37% respectively. Plasma non-esterified fatty acid levels were significantly higher in the diabetics (0.47 mmol/l) than in the non-diabetics (0.26 mmol/l). Coefficients of variation were 46% and 33% respectively. Two conclusions can be drawn; first, when near normal mean values for blood glucose are achieved, other metabolite and hormone levels are also near normal; second, even when the available means for diabetic control, strict diet and insulin-mixtures twice daily, are used at their maximum, metabolism in diabetics is more unstable than in non-diabetics.  相似文献   
8.
Summary Serum growth hormone values in 37 patients with diabetic ketoacidosis were 5.4±0.8 ng/ml (S.E.M.) in males and 6.7±1.1 ng/ml in females before treatment; while in five hyperosmolar non-ketotic patients the HGH concentration was 3.9±0.5 ng/ml. One hour after insulin 90% of patients showed a rise in HGH, to a mean of 33.7±9.8 ng/ml for males and 25.5±6.0 ng/ml for females in ketoacidosis; and to 27.1±9.9 ng/ml for hyperosmolar coma patients. The rise, which was transient, was inversely correlated with pretreatment plasma glucose, the l h plasma glucose concentration and plasma urea, and directly proportional to the % fall in blood glucose after 1 h. When the ketoacidosis patients were divided into two groups according to HGH response, those with a small response had the greater disturbances of plasma glucose, blood ketone bodies, blood lactate, plasma urea, blood pH, and blood pressure, the smaller 1 h fall in blood glucose, and the higher mortality. Thus the most severely ketoacidotic patients had the poorest growth hormone response. Growth hormone is probably of little importance as an insulin antagonist in diabetic coma.Presented in part at the Spring Meeting of the British Diabetic Association, York, April 1972.  相似文献   
9.
ABSTRACT— We studied the relationship between the portal blood flow velocity and the arterial ketone body ratio in patients with chronic liver disease receiving a dobutamine infusion. We used an ultrasonic Doppler duplex system to evaluate the portal blood flow velocity. Dobutamine was given intravenously at 5 μg/kg/min for 20 min. Dobutamine infusion induced smaller changes in the portal blood flow velocity and ketone body ratio in liver cirrhosis than in chronic hepatitis. The existence of shunts and the poor increase of the cardiac index in response to dobutamine explained the limited improvement of portal blood flow velocity in cirrhosis patients. The ketone body ratio was improved by dobutamine in cirrhosis patients whose portal blood flow velocity was increased by more than 10%, while this ratio decreased when the increase of it was less than 10%. There was no change in portal oxygen extraction in the cirrhosis group, and portal oxygen uptake only increased when the portal blood flow velocity rose by more than 10%. Dobutamine should only be used to treat liver failure if the portal blood flow velocity is increased by more than 10% or the arterial ketone body ratio is improved by a test infusion.  相似文献   
10.
Summary It is controversial as to whether ketone bodies are utilized by the human brain as a fuel alternative to glucose during hypoglycaemia. To clarify the issue, we studied 10 normal volunteers during an experimental hypoglycaemia closely mimicking the clinical hypoglycaemia of patients with Type 1 (insulin-dependent) diabetes mellitus or insulinoma. Hypoglycaemia was induced by a continuous infusion of insulin (0.40 mU·kg–1·min–1 for 8 h, plasma insulin 180 pmol/l) which decreased the plasma glucose concentration to approximately 3.1 mmol/l during the last 3 h of the studies. Subjects were studied on two occasions, i. e. spontaneous, counterregulatory-induced post-hypoglycaemic increase in 3--hydroxybutyrate (from 0.2 to 1.1 mmol/l at 8 h), or prevention of post-hypoglycaemic hyperketonaemia (plasma -hydroxybutyrate 0.1 mmol/l throughout the study) after administration of acipimox, a potent inhibitor of lipolysis. In the latter study, glucose was infused to match the hypoglycaemia observed in the former study. The glycaemic thresholds and overall responses of counterregulatory hormones, symptoms (both autonomic and neuroglycopenic), and deterioration of cognitive function (psychomotor tests) were superimposable in the control study in which ketones increased spontaneously after onset of hypoglycaemic counterregulation, as compared to the study in which ketones were suppressed (p=NS). The fact that responses of counterregulatory hormones, symptoms and deterioration in cognitive function were not exaggerated when posthypoglycaemic hyperketonaemia was prevented, indicate that during hypoglycaemia, the counterregulatory-induced endogenous hyperketonaemia does not provide the human brain with an alternative substrate to glucose. Thus, it is concluded that during hypoglycaemia, endogenous hyperketonaemia does not contribute to brain metabolism and function.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号